1. Field of the Invention
The present invention relates generally to switches and, more specifically, the present invention relates to semiconductor switches that are coupled to control circuits.
2. Background Information
Electronic circuits using switches coupled to control circuits typically have to be designed to meet cost targets defined at the start of a design. The control circuitry used to control the switching of the switches can be a significant part of the electronic circuit cost and any way to reduce the cost of this circuitry is therefore a benefit.
One circuit configuration using switches coupled to control circuits is a power conversion circuit called a half bridge converter. This circuit typically has two switches configured in a half bridge wherein one switch is referred to as a high side switch and the other is referred to as a low side switch as will be known to one skilled in the art.
The control of power delivery to the load in this type of circuit is typically achieved by a control circuit controlling the period of time for which each switch is on within a switching cycle. This on time period is typically controlled in response to a feedback signal received from a sense circuit coupled to the load. The frequency of the switching, being the reciprocal of the time between the start of one on time period and the start of the next on time period of one of the switches, is determined either by an oscillator forming part of the control circuit or a resonant frequency of the load circuitry coupled to the low side and high side switches.
In circuits where the oscillator forms part of the control circuit, turn on and or turn off signals are typically coupled to the high side switch in the half bridge by level shift circuitry, as will be known to one skilled in the art, which adds significant cost to the overall half bridge circuit. In circuits where the frequency of switching is determined by a resonant frequency of the load circuitry coupled to the low side and high side switches, the turn on and or turn off signals can again be coupled to the high side switch by level shift circuitry or using inductively coupled drive signals, which typically sense the current or voltage at the load to determine the time at which to turn on the low side and high side switches.
Since the inductively coupled drive signals can be coupled with separate windings and therefore individually referenced to the low side and high side switch control circuits, the requirement for other level shift circuitry is eliminated. However, the inductively coupled element is required which is coupled to the load and the control circuitry for both low side and high side switches, which again adds cost to the overall half bridge circuit.
In other configurations, inductively coupled drive signals can be used to determine the start of an on time period of either the high side or low side switches and individual oscillators coupled to both low side and high side switches are used to determine the time at which the low side or high side switches are turned off. Again, in these configurations, an inductively coupled drive circuit and an oscillator or timing circuit is required for both high side and low side switches, which adds cost. The same limitations apply to full bridge circuits and other configurations requiring a high side switch.